The invention relates to a method for querying a database.
Such methods for querying databases are used to obtain information that falls within a certain search pattern. The databases store not only the data contents, such as measurement data, picture data, etc., but also characteristics, or so-called meta data, which characterize the data contents. In a database query, these characteristics, which satisfy the conditions of the query can thus be used, among other things, to classify the database content.
To be able to formulate such classification criteria, however, the physical memory structure of the characteristics and their semantic meaning has to be known.
Thus, the drawback is that corresponding requesting clients are always written for a specific database with a defined structure. If a user wants to direct an inquiry or query to a database, he must therefore know the corresponding client or query program or the data structure of the database.
In a query to a single database, a special client program for that database is therefore normally used. In case of a connection to the database via a network (LAN or WAN, Internet, etc.) the client program is loaded onto the client computer upon logging into the database, for example as a plug-in for a browser.
In contrast, if several databases are to be addressed simultaneously, this is realized via a corresponding interface, or middleware, of a server or a database. Several clients (or wrappers) are realized in the middleware on the server or in a database. The client is defined for the middleware. Since the wrappers are implemented in the middleware, the disadvantage is that only those databases that were previously analyzed with respect to their data structure and API (Application Program Interface) can be integrated via the middleware.
As a consequence, the known methods for querying databases depend on the latter's data structure to the extent that the respective structure of a database must be known for a query. This has the drawback that a query of a database is made more difficult, particularly if its exact structure is unknown to the inquirer.